The disclosure of Japanese Patent Application No. 2000-322581 filed on Oct. 23, 2000, including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a fuel injection valve body for a direct injection type internal combustion engine, in which fuel is injected directly into a combustion chamber of the internal combustion engine.
2. Description of Related Art
A direct injection type internal combustion engine, provided with a fuel injection valve that injects fuel directly into a combustion chamber, executes stratified charge combustion by injecting fuel into the combustion chamber during a compression stroke, thereby improving fuel economy. In stratified charge combustion, it is necessary that fuel injected from the fuel injection valve forms layered rich fuel-air mixture, and that the layered rich fuel-air mixture reaches an ignition plug at an ignition timing. For this reason, it is important that the shape and direction of fuel injected from a nozzle hole of the fuel injection valve body be accurately maintained to ensure a stabilized operation of the internal combustion engine.
If deposits accumulate in the nozzle hole, however, the shape and direction of fuel injected from the nozzle hole may be changed. In such cases, it becomes impossible for layered rich fuel-air mixture to reach the ignition plug at the ignition timing, resulting at times in an unstable operation of the internal combustion engine. The term xe2x80x9cdepositsxe2x80x9d used herein refers to an oxide or a carbide produced when fuel and/or oil are burnt.
Since accumulation of the deposits depends on the temperature of the nozzle hole, as described in, for example, Japanese Patent Laid-Open Publication No. 09-264232, it is important to control the temperature of the nozzle hole to ensure accurate fuel injection. However, the conventional fuel injection valve body for direct injection type internal combustion engines has been insufficient to control the temperature of the nozzle hole. For example, in a conventional fuel injection valve body for direct injection type internal combustion engines as shown in a front view in FIG. 10A and a longitudinal sectional view in FIG. 10B, only a central portion 153a of a nozzle body tip portion 153 exposed to an interior of the combustion chamber protrudes in a conical shape. On the contrary, a peripheral portion 153b is not protruded, therefore, a right-angle corner portion 153d is formed between a nozzle body outer peripheral surface 153c and the peripheral portion 153b. As a result, heat generated by combustion easily concentrates from the periphery at the corner portion 153d. The heat at the corner portion 153d is conducted to a nozzle hole 154, and the temperature thereof also easily increases, resulting in more likelihood of promoting accumulation of deposits. Moreover, a recessed portion 153e formed between the protruding central portion 153a and the peripheral portion 153b enlarges the surface, and heat generated by combustion even further increases the temperature of the corner portion 153d and the central portion 153a through the enlarged surface. This increases the temperature of the nozzle hole 154 even further, thus promoting accumulation of deposits.
Another conventional arrangement is shown in a front view in FIG. 11A and a longitudinal sectional view in FIG. 11B, in which an entire nozzle body tip portion 203 exposed to an interior of the combustion chamber is protruded in a conical shape. However, a central portion 203a is further protruded from a tip surface 203c of a peripheral portion 203b. Therefore, a recessed portion 203d is formed between the protruding central portion 203a and the tip surface 203c of the peripheral portion 203b. This results in that heat generated by combustion even further increases the temperatures of the peripheral portion 203b and the central portion 203a through a surface enlarged by the recessed portion 203d. This causes a problem that the temperature of the nozzle hole 204 easily increases, thus promoting accumulation of deposits.
In order to solve the foregoing problems, it is an object of the invention to provide a fuel injection valve body for a direct injection type internal combustion engine that can control the temperature of a nozzle hole.
To achieve the foregoing object a fuel injection valve body for a direct injection type internal combustion engine injects fuel directly into a combustion chamber of the internal combustion engine, according to one aspect of the invention, is shaped such that an entire nozzle body tip portion formed with a nozzle hole and exposed to an interior of the combustion chamber is formed into a protruded shape without forming a corner portion or a recessed portion on a surface thereof.
If the nozzle body tip portion is not formed such that the entire nozzle body tip portion is protruded and free from a corner portion, heat generated by combustion tends to concentrate at the corner portion. The temperature of the nozzle hole, therefore, tends to increase because of heat conduction from the corner portion, thus promoting accumulation of deposits. When there is a recessed portion on the surface thereof, heat generated by combustion increases the temperature of the nozzle body tip portion is conducted from the surface enlarged by the recessed portion and, which results in easily increasing the temperature of the nozzle hole. This again in turn promotes accumulation of deposits.
Contrary to that, if the entire nozzle body tip portion of the fuel injection valve body is formed into a protruded shape without forming a corner portion or a recessed portion on the surface thereof, no corner portions are formed and the surface is not unnecessarily enlarged. As a result, the temperature of the nozzle hole can be prevented from increasing and accumulation of deposits can be restricted.
To achieve the foregoing object, a fuel injection valve body for a direct injection type internal combustion engine that injects fuel directly into a combustion chamber of the internal combustion engine may comprise a nozzle body tip portion which forms a nozzle hole therein and is exposed to an interior of the combustion chamber, and a cap disposed on a periphery of the nozzle body so as to secure the nozzle body onto a main body side of the fuel injection valve body. In this arrangement, a continuous tip portion is formed of the nozzle body tip portion and tip of the cap. The entire continuous tip portion is formed in a protruded shape without forming a corner portion or a recessed portion on a surface thereof.
The continuous tip portion prevents the temperature of the tip portion of the cap from increasing, thus preventing the temperature of the nozzle body tip portion from increasing through heat conduction from the tip portion of the cap. Therefore, the temperature of the nozzle hole can be prevented from increasing and accumulation of deposits can be restricted.
To achieve the foregoing object, according to a yet further aspect of the invention, a fuel injection valve body for a direct injection type internal combustion engine that injects fuel directly into a combustion chamber of the internal combustion engine may be provided, wherein a part of a nozzle body tip portion, in which a nozzle hole is formed and which is exposed to an interior of the combustion chamber, is covered through a gap with a tip portion of a cap, which is disposed on a periphery of the nozzle body so as to secure the nozzle body onto a main body side.
The arrangement, in which a part of the nozzle body tip portion is covered with the tip portion of the cap through the gap, reduces a part of the nozzle body tip portion that is exposed to combustion flame, which prevents the temperature of the nozzle body tip portion from increasing. In addition, thanks to the gap, heat is not directly conducted to the nozzle body tip portion even when the temperature of the tip portion of the cap increases, which effectively prevents the temperature of the nozzle body tip portion from increasing caused by heat transfer from the tip portion of the cap. Therefore, the temperature of the nozzle hole can be prevented from increasing and accumulation of deposits can be restricted.